[Impressions of Truth]

Bullets. Screwdrivers. Fingernails. In this lab, every mark tells a story.

Practically anything can leave a mark on something slightly softer: a screwdriver prying open a cash register drawer. A gas pedal slamming into the bottom of a shoe. A knife rupturing the rubber of a tire. The barrel of a gun scraping against a bullet that is hurtling through it.

These are the kinds of impressions studied by seven scientists in the Firearms and Tool Mark Identification section of the Virginia Division of Forensic Science. Working for medical examiners, commonwealth's attorneys and law enforcement officials across the state, they investigate marks. They identify them, measure them and match them on the third floor of Biotech II, a $30 million, 135,000-square-foot building at Fifth and Jackson streets behind the Richmond Coliseum.

This is not the headline-grabbing world of DNA. Rarely is there any bodily fluid  most DNA evidence has already been lifted before it reaches this floor. There are no bodies  they enter the opposite end of the building, bound for the medical examiner. There is no drug-testing equipment. No fingerprint-lifting. Few test tubes. Rather, scientists focus on something much more ordinary: shadows.

Shadows show lines. Ridges. Grooves. Striations. Seven examiners study and map such territory as carefully as Lewis and Clark. It is an intense job: They are pressed for time. There is no room for error. They must stand behind their work. And often, their findings will mean the difference between a verdict of guilt or innocence.

Take the fingernails, for example. In 1991, an armed robber grabbed for cash in the cash register drawer of a convenience store in Sussex. He pulled out money and in the process broke one of his nails. The Richmond lab asked the suspect, Joseph Cotton, to grow his nails. They compared the lines underneath his fingernail with the lines on the nail found in the register drawer. The mountains matched. He was guilty.

Impressions are everything.

cott Glass is trying to read a crowbar.

Henrico County police found the black metal tool in a suspect's car. Detectives think it may have been used to pry open the back door of a gas station in a series of breaking-and-enterings. Glass reaches for a tube of something called Mikrosil.

Back in college, Glass studied Aristotle and the Constitution, earning a political science degree that he figured would lead him to law school. Instead, he pursued a graduate degree in criminal justice. Outside the classroom, he worked part time in the Northern Virginia lab of the Virginia Division of Forensic Science, one of the four regional labs across the state. He filed and typed  and watched how examiners in the tool-mark section matched such things as the markings on a discharged cartridge case to the specific gun that fired it.

He became fascinated with forensic science. It helped that his fiancee, Samantha, was into it, too. Glass completed his graduate degree and entered the two-year training program to become a certified examiner  one of about 800 in the world. Now Glass, 32, has been in the state's central lab in Richmond for seven years. (Samantha, now his wife, works here too, as a forensic scientist on another floor.)

Like the other examiners here, Glass spends his time working on details. He must think creatively, but follow steps logically from one point to the next, using scientific method, all the while knowing that sometimes he will end up with no answer at all.

"We tell our students it's better to do things slowly and well," says Ann Lee Davis, who with her colleague, section chief, James L. Pickelman, supervises this section and teaches forensic science at Virginia Commonwealth University.

A serious error like identifying a marking incorrectly, Davis says, "could take you out of the field forever. You might as well hang it up."

Glass feels the pressure. "It is stressful because we don't want to make mistakes," he says. He adds that there is comfort in the checks and balances in place  and in peer review. But the impatient need not apply.

This crowbar case, for example, seems to take up much of an afternoon. There are plastic 35 mm film canisters on Glass's desk. Inside them are casts of the indentations on the gas station's back door, taken by police at the crime scene.

Gripping the crowbar that police think may have made the indentations, Glass scrapes it across different squares of lead a little larger than a postage stamp. He varies the angle and pressure ever so slightly, hoping to somehow replicate the movement the burglar may have used against the frame of the gas station door.

Angles are important. Scrapes against the lead will look different at every 17 degrees the tool is held against it.

Now Glass must start to compare. Because he has only casts of the door impressions with which to compare his own test marks  the inverse of what he needs  he must make casts of his impressions, too.

For that, he uses Mikrosil. It's a sort of red-colored gunk, a silicon-based gel that hardens quickly. Glass smears some of it over the impressions he made, waits for it to dry and peels it off. Then he moves to his $80,000 Leica comparison microscope. All the examiners have one. It allows them to see magnified versions of two things simultaneously through one eyepiece.

Glass places one of the casts he made on one of the microscope's trays. He puts a cast the police made on the other. With his eyes fixed against the eyepiece, he slowly adjusts each sample, turning it so the light hits it just so. First, the striations must face the same direction. Then he slowly dials a knob on the scope, which moves a line back and forth between the two images. Glass should be able to see if one side matches the other.

But he reaches no immediate conclusion. "I'm having a bit of difficulty getting good test marks," he says. He starts over. He will need to use the crowbar to make more scrapes against lead. Make more casts. Stare at the scope again.

But even if he finds a match, how can Glass prove that it was this particular crowbar used in the breaking-and-entering? Didn't some crowbar company make hundreds of these tools, exactly alike, churning them out with assembly-line precision? You could probably buy the same kind of crowbar at a hardware store in Richmond, Calif.

True, Pickelman says. The tools look the same to the naked eye. But each crowbar is different, he says  even if it was born on the assembly line on the same day, right next to another. "Our whole science is based on: No two things man-made are identical."

Or are they? Some people are starting to question that in court.

"Our job as attorneys is to question everything," says Steven D. Benjamin, a Richmond defense attorney. He teaches scientific evidence at the University of Richmond's School of Law and is a director of the National Association of Criminal Defense Lawyers.

"If a scientific discipline is bogus or based upon junk notions," Benjamin says, "it is our job to reveal that. And the fingerprint controversy has been a good example."

Yes, fingerprints. They have long been accepted as proof that someone was somewhere  that theirs was the hand on the knife, the finger on a gun. It is as basic as Barney Fife. Yet fingerprints are under fire.

It started with a case taken up by the U.S. Supreme Court in 1993, Daubert v. Merrell Dow Pharmaceuticals. Lawyers for the plaintiff claimed that a child had suffered from birth defects as a result of a drug manufactured by Merrell Dow. The company balked, claiming there was no evidence to prove that.

After studying the claims, the Supreme Court for the first time significantly cracked down on the use of expert witnesses in federal courts. The court made it clear that experts could no longer testify based on notions that were "generally accepted" in their field. Instead, the court asked judges to act as the "gatekeepers" of science, following a series of guidelines that would help establish the reliability of scientific evidence.

Such questions were important: Had the science been tested thoroughly? Subjected to rigorous academic study? Was there a potential error rate?

DNA is a good example of a science that has gone through this testing. But the long-established notion of fingerprints, perhaps because they were so ingrained, only came under scrutiny in January. A federal judge applied the Daubert decision to testimony about fingerprints. It has caused the forensic-science community to seriously scrutinize how they can prove fingerprint matching is reliable in court.

The Daubert decision has probably affected handwriting identification even more, says Jennifer L. Mnookin, a University of Virginia law professor who specializes in expert evidence.

"This is making, I would guess, all of the forensic scientists a little bit nervous," Mnookin says, "because traditionally forensic sciences haven't been linked with university research departments; they haven't gone about proving their science in very systematic ways."

The question Daubert raises, she says, is how reliable science has to be before it is allowed in court. She says forensic science isn't in danger; it's just that there may be more empirical studies advanced to shore up testimony.

In the Richmond lab, Davis  just elected first vice president of the Association of Firearms and Tool Examiners  has no doubt her science is sound. She points to scores of studies that already exist. If questioned by the courts, she says, "I think that we're ready for them if they do."

She also agrees that the forensic science community will  and is  conducting more studies to secure the field. After studying the evidence, she says, "any qualified and honest examiner should reach the same conclusion." But, she adds, "no amount of science, no amount of studies, no amount of research is going to keep people from giving bad opinions."

And that, Davis says, is what the judiciary must do: Keep incompetent people from testifying. And rely on true science.

Jim Pickelman and Ann Davis are veterans of the Firearms and Tool Mark Identification section. You could say they are from the years B.C.  that is, Before Cornwell. They knew Patricia when she worked in their halls, before she became that famous crime novelist whose books are filled with Richmond references.

They were also here when they were the only staff. And you quickly get the sense that they are used to each other. Davis knows when Pickelman has cracked a joke. Pickelman knows that Davis enjoys talking about her work. They are familiar. Davis pops in Pickelman's office to pour him what's left of the coffee  so she can make a fresh pot. And when Davis can't find something she'd like to show a visitor, Pickelman jumps in. "I got one here, Annie," he calls out.

Yet they are straightforward, thoughtful and serious about their work. Glass has seen them pass their knowledge along. "Pretty much everything I've learned," he says, "I've learned from those two."

Davis, who turns 48 in September, joined the lab's firearms division in 1984. She earned her degree in biochemistry from Queens College in Charlotte, N.C. "And I ended up getting married instead of going to med school," she says. Among the collection of Teenie Beanie Babies she keeps in her office is a baby bat her children gave her named "Batty." It's one of her favorites.

Pickelman, a former Marine, is 63, but he isn't too old to wear a pink dress shirt. He started his career as a Michigan state trooper for five years before moving into the state's police lab. He stayed there for 20 years, retired in 1988, then came to work here. He was computer illiterate  which wasn't a problem because the office didn't have computers. Technology, of course, is different today. "It has progressed at light speed in my career," he says.

So has forensic science  and its place in the courtroom.

"We wouldn't be able to function without them," says Lin Tyler, a Richmond Police sergeant who supervises the forensic team. There are eight detectives and technicians in her department, she says. And "every case they go out on, something ends up at the lab. We probably talk to them every day."

Their behind-the-scenes field is only growing, Tyler says.

That is evident from Davis and Pickelman's lab, which the two of them designed before Biotech II opened in 1998. Ten years ago, they say, they couldn't have imagined needing six bays  a sort of lab-appropriate cubicle space for each examiner  much less needing extra room for a new examiner starting this month.

The layout provides areas for specific purposes, like rooms in a house.

There is the office, where examiners share a typical kind of workspace, with phones and computers  and shelves of manuals and gun catalogs.

There is the library, where about 8,000 revolvers, rifles, shotguns and semi-automatics hang along moveable shelves. It is practically a museum, stocked with nearly every brand and type of ammunition that exists.

Near the library is a kind of dad's garage, a tool lab where examiners can make parts, put parts together or take parts apart. A not-so-sexy Craftsman tool calendar hangs on the wall.

There is also a rec center of sorts. It includes a 50-foot firing range, with a trap that catches and slows down bullets by spinning them around and around a drum, then dropping them into a trough. Examiners can also shoot into a steel tank filled with about 4 feet of water. They retrieve the bullets from the tank to compare the marks left by the gun.

Most of the work takes place in the lab area, which has the feel of a large, advanced college science classroom. Down the sides, there are bays in which examiners work. They feature curtains that can be drawn to regulate light as the scientists look through their microscopes. In the middle, between the bays, a large table provides common workspace.

And nowhere in particular, an odds-and-ends array of stuff: a container of cotton swabs. A measuring tape. Boxes of Hefty One-Zips. A mallet. Butcher paper on a roll. A can of WD-40.

And in the corner, there is a new $1 million computer paid for by grants from the federal Bureau of Alcohol, Tobacco and Firearms.

The computer station, a piece of Canadian-made equipment called IBIS, is part of the National Integrated Ballistic Information Network, or NIBIN. It reflects the increasing need to speed up the work of firearms examiners and to link crimes that may have been committed in different jurisdictions.

Examiners take bullets or cartridge cases found at the crime scene and put them under a microscope attached to the computer. They can also use ammunition they shoot from a firearm in question. The computer records the striations and adds it to a networked database. Examiners can then narrow down potential matches from other crimes in the state  or elsewhere.

Just as the crowbar left a unique pattern on the gas station door, guns leave unique patterns. Inside the barrel of a gun are microscopic surface features within the metal, Pickelman explains. There are also characteristics that control the bullet's pattern of flight. When the bullet is fired, it expands, and as it passes through the barrel it naturally grazes that metal, Pickelman says, leaving "literally hundreds of tiny scratches, or stria."

In the case of a cartridge, its story is found on its back. When the firing pin strikes it, there is a tiny explosion. As the bullet shoots out the barrel, the cartridge case is forced backward, into the breach of the gun. On that cartridge, scientists can see a pattern of ridges and a firing-pin impression, both of which help identify the individual firearm.

In the late '80s, when Pickelman and Davis were the only two examiners here, they remember making matches by memory. "We would only know what was going on in Richmond," Pickelman recalls. The two would cover the walls with 4-by-5 photographs of enlarged breach-phase marks and bullet striations. Virginia started using an early computer-matching system in 1993, but only recently has a national system been selected as a standard.

Ferrara says it has already had hits. "It's like a DNA databank," he says, "except it's like one for guns instead of people."

Whatever computers are used to find potential matches, though, the law holds that examiners must go back to look at the original evidence to determine whether a match can be made. A human must come up with the final answer.

Attorney Benjamin says lawyers will continue to raise the questions about those answers. "Juries are increasingly looking for science in the courtroom to answer the question, 'What occurred in this case?'" he says.

And even as forensic scientists hunch over their microscopes in the Richmond lab, they know their courtroom appearances are ultimately where they prove themselves. So they measure with precision. Vigorously study details. Answer their own questions without doubt before a lawyer is paid to trip them up.

Davis still gets nervous, she says. "You can't just say, 'Because I said so,' That's not good enough," she says. And examiners are truly on their own on the stand. "They're an island right then at that moment in time." S